How to convert a date to YYYYDDD?

Question

I can't figure out how to turn Sys.Date() into a number in the format YYYYDDD. Where DDD is the day of the year, i.e. Jan 1 would be 2016001 Dec 31 would be 2016365

Date <- Sys.Date()  ## The Variable Date is created as 2016-01-01
SomeFunction(Date)  ## Returns 2016001

Answer 1

You can just use the format function as follows:

format(Date, '%Y%j')

which gives:

[1] "2016161" "2016162" "2016163"

If you want to format it in other ways, see ?strptime for all the possible options.

Alternatively, you could use the year and yday functions from the data.table or lubridate packages and paste them together with paste0:

library(data.table) # or: library(lubridate)
paste0(year(Date), yday(Date))

which will give you the same result.

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The values that are returned by both options are of class character. Wrap the above solutions in as.numeric() to get real numbers.

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Used data:

> Date <- Sys.Date() + 1:3
> Date
[1] "2016-06-09" "2016-06-10" "2016-06-11"
> class(Date)
[1] "Date"

Answer 2

Here's one option with lubridate:

library(lubridate)
x <- Sys.Date()
#[1] "2016-06-08"
paste0(year(x),yday(x))
#[1] "2016160"